XSPC has no problem with any GPU block, and its pump still handle 1 more GPU block.
I personally have an experience of adding 1 VGA, and it works no problem.
I saw someone even doing 1 CPU, 2 radiator, 3 SLI with this pump.
I think this is little overkill but I am pretty sure that XSPC 750 pump(the pump in the rasa kit) can handle
1 more VGA.
What you need to buy for adding GPU on your loop are a VGA/GPU
block and 2 barbs(+2 clamps) or 2 Compression fittings.
Don't forget you need to buy compatible GPU block with your VGA, not your RASA kit.
Look my post. It will explain all what I want to say about RASA kit.